rich deposits of hydrocarbon mixtures that formed from the remains of organisms (p. 267, p. 462)
the way a mineral breaks, determined by the mineral's crystal structure (p. 668)
a system of objects that are not moving with respect to one another (p. 328)
the movement of an object toward Earth because of gravity (p. 343)
the number of complete cycles per unit time for a periodic motion (p. 504)
a method of transmitting a radio signal in which the frequency of the carrier wave varies while its amplitude remains the same (p. 541)
a force that opposes the motion of objects that touch as they move past each other (p. 359)
a sharply defined boundary that forms when two unlike air masses meet (p. 767)
the fixed point a lever rotates around (p. 428)
an atom or group of atoms that determines the properties of an organic compound (p. 272)
a device that prevents overheating due to current overload in a circuit (p. 612)
a nuclear reaction in which the nuclei of two atoms combine to form a larger nucleus (p. 315)
G
- galaxy
a huge group of stars, star systems, star clusters, dust, and gas bound together by gravity (p. 848)
- galvanometer
a device that uses an electromagnet to measure small amounts of current (p. 638)
- gamma ray
a penetrating form of radiation emitted by an unstable nucleus (p. 294)
- gas
the state of matter in which a material has neither a definite shape nor a definite volume (p. 70)
- gas giant
a large, massive planet (such as Jupiter, Saturn, Uranus, or Neptune) that is composed mainly of hydrogen and helium (p. 811)
- generator
a device that converts mechanical energy into electrical energy by the relative motion of a coil of wire with respect to a magnetic field (p. 643)
- geocentric
a description of a model of the solar system in which all of the planets revolve around Earth (p. 791)
- geologists
scientists who study Earth and the processes that have shaped Earth over time (p. 660)
- geology
the study of the origin, history, and structure of Earth (p. 4)
- geothermal energy
thermal energy beneath Earth's surface (p. 464)
- giant
a large, massive, bright star that is somewhat smaller and fainter than a supergiant (p. 839)
- glacier
a large mass of ice and snow moving on land (p. 706)
- global warming
an increase in the temperature of Earth's lower atmosphere, caused in part by increased levels of carbon dioxide or water vapor (p. 782)
- global wind
a wind that blows over long distances from a specific direction (p. 758)
- globular cluster
a large spherical-shaped group of older stars that usually lacks sufficient amounts of gas and dust to form new stars (p. 847)
- gravitational force
an attractive force that acts between any two objects (p. 380)
- gravitational potential energy
potential energy that depends upon an object's height above a reference point (p. 449)
- gravity
the attraction between any two objects because of their masses (p. 361)
- greenhouse effect
a process in which gases in Earth's atmosphere, such as water vapor and carbon dioxide, allow visible light to pass through but absorb reradiated infrared radiation that warms the lower atmosphere (p. 755)
- ground state
a state in which all the electrons in an atom have the lowest possible energies (p. 118)
- grounding
the transfer of excess charge through a conductor to Earth (p. 613)
- groundwater
the fresh water found beneath Earth's surface within cracks and among particles of rock and soil (p. 704)
- group
a column of elements in a periodic table (p. 131)
H
- half-life
the time required for one half of a sample of a radioactive isotope to decay (p. 299)
- halogens
the elements in Group 7A of the periodic table (p. 144)
- hardness
the resistance of a mineral to scratching (p. 668)
- heat
the transfer of thermal energy from one object to another because of a difference in temperature (p. 474)
- heat engine
any device that converts thermal energy into work (p. 483)
- heat of fusion
the energy a substance must absorb in order to change from a solid to a liquid (p. 86)
- heat of vaporization
the energy a substance must absorb in order to change from a liquid to a gas (p. 88)
- heat pump
a device that uses work to transfer thermal energy from a colder area to a warmer area (p. 490)
- heliocentric
a description of a model of the solar system in which Earth and other planets revolve around the sun (p. 791)
- hertz (Hz)
the unit of measure for frequency, equal to one cycle per second (p. 504)
- heterogeneous mixture
a type of mixture in which the parts of the mixture are noticeably different from one another (p. 41)
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